Share prices rose across the industry after four airlines said they will save hundreds of millions of dollars in fuel costs starting this year, with global oil prices down more than 57 percent since June. The carriers said they plan to use the fuel savings to pay down debt and return cash to shareholders. On Thursday, Southwest Airlines (LUV.N) estimated it would save $1.7 billion on fuel in 2015. Delta Air Lines (DAL.N) tallied its 2015 savings at more than $2 billion, while fuel price forecasts from United Airlines (UAL.N) and Alaska Airlines (ALK.N) promised similar cost reductions.